Filament and method of manufacture thereof



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mensa Dec. 1s, 1'925.

UNITED STATES PATENT OFFICE.

GOBTON E. FONDA, OF SCHENECTADY, NEW YORK, ASSIGNOB TO GENERAL ELECTRICCOMPANY, A CORPORATION OF NEW YORK.

FILAMENT AND METHOD OF MANUFACTURE THEBEOF.

Application led July 29, 1920. Serial No. 399,798.

To all whom tmay concer/n.-

Be it known that I, GoR'roN R. FONDA, a citizen of the United States,residing at Schenectad in the county of Schenectady,

' 6 State of 4ew York, have invented certain new and useful Im rovementsin Filaments and Methods of anufacture Thereof, of which the followingis a specification.

The present invention relates to the production of ilamentary orwire-shaped bodies, strips, sheets or the like, of tungsten alloy, as,for example, filaments for incandescent lamps, electron dischargedevices and the like.

Although metallic tungsten cannot be worked mechanically by themetallurgical methods applied to other metals, it can be renderedductile and drawn into fine filamentary form by the methods described in`il() Coolidge Patent 1,082,933. It is advantaeous to constitutefilaments for incandescent amps, or other devices, of an alloy oftungsten. For example, in my prior Patent 1,496,457, 'issued June 3,1924, I have described lamentary conductors consisting of Y tungstenVcontaining iron not in excess ofl about one or two per cent of thetotal. In some cases, the mechanical working of alloys of tungsten,such, for example, as tungstenironalloys, is attended with diiiculties.

` In accordance with my present invention, I have provided a new methodof preparing wires or filaments of alloys, or solid solutions, of arefractory metal, for example, tungsten, and one or more alloyingmetals.

As described more fully hereinafter, filamentary bodies are'prepared inaccordance with this invention by depositing alloying metal byelectrolysis or other convenient 40 method on a clean surface of a bodof refractory metal, which has alrea yy been drawnor otherwise workedeither into final desired form or into a form suitable for sub-v sequentworking.

As" illustrative of my invention, I will describe in detail a continuousprocesslfor carrying outthe preparation of alloy filaments of tun tenand iron, although it to be un erstood that my invention is l0applicable to alloys of tungsten or other refractory' metal withelements other than wish surface impurities, such as grease and carbon,for example, by heating the filament in a protective environment to atemperature of about 1000 to 13000 C., preferably to aboutv 12000 C. Asillustrated in Fig. 1, a filament or -wire 1 may be drawn from a reel 2over revolving electrical contacts 3, 4 in a container 5 into which aprotective gas, such, for example, as hydrogen, is introduced by aconduit 6. A suitable heating current for the wire 1 is conveyed to thecontacts 3, 4, by the conductors 7 8, which may be connected to a sourceS.

The cleansed wire or filament is introduced into a suitable electrolyte,for example, a solution of ferrous chloride or ferrous ammoniumsulphate. Although proportions may be varied, I prefer to use by weightabout 200 parts of ferrous chloride or of ferrous ammonium sulphate to1000 parts of water. Preferably 50fparts of magnesium sulphate and 5parts of sodium bicarbonate may also be added to the electrolyte. Asfurther illustrated diagrammatically in the drawing, the wire l1 to becoated with iron is slowly passed through electrolyte over pulleys 9, 10supported by a standard 11. The wire 1 is connected as cathode to asuitable source of direct current G by the conductor 12, the anode 13consisting of iron, carbon, or other suitable material, being connectedto the positive conductor 14. The current is chosen to produce a currentdensity of about 0.003 amperes per square centimeter of surface. Thecoated wire or filament is passed over another pulley 15 into areceptacle 16 vcontaining pure water. It is then dried as by passingthrough a dryer 16 and finally wound upon a spool 17 driven by a motor18 through suitable speed reducing gears 19. The coated wire is pliableand rugged. It desired, it may be stored forfuture use.

As shown in Fig. 2, the coating 20 upon the core 21 represents suchrelatively inconsiderable part of the total mass of the Wire or filamentthat the production by the described method of a homogeneous alloy issurprising, articularly so as the alloying metal is app ied externally.I do not intend to represent exact proportions of core and coating. Infact, the proportions-may be varied, but l mean to show only roughly thegeneral relative magnitudes of the core and coating. As indicated, thecore largely preponderates in mass over the coating. My investigationsindicate that the coating metal diffuses uniformly throughout the coremetal during the alloyin step. The resistance characteristics of t eresulting alloy correspond to the characteristics of a homogeneous alloyof the same proportions. The small diameter or thinness of a filament orribbon favors this result. Contrary to what might be expected, thealloying step in the case of the present process requires a materiallyshorter time than the process of making alloy filaments or the likedescribed in my prior Patent No. 1,496,457, referred to above, accordingto which the alloying metal is mixed in a state of fine subdivision withthe refractory metal.

Alloyage of the core and coating is produced by heating the compositeWire to a temperature of at least about 15009 C. A1- though preferable,it is not absolutely essential in all cases that this alloying step becarried out separately preparatory to the manufacture of a lamp or otherdevice in Which the Wire or filament is to be used. ln the case of thefiner filaments particular- 1y, the composite filament may be mounted ina lamp bulb in the usual Way and the lamp may be exhausted and sealed.When the lamp is put into use the heating of the filament toincandescence at the usual operating temperature or sometimes by apreliminary heating at a lower temperature Will cause cementation orabsorption of the iron coating by the tungsten core. For example, l haveobtained good results by heating a four mil filament for five minutes toabout 1600o C. which is above the melting point of irorli The resultingfilaments are operable in mps at a highlighting efficiency Withoutblackening.

y invention is not restricted to the electr ytic deposition of analloying metal; for example, when it is desired to produce an alloy oftungsten With zirconium the desired amount-of zirconium may be depositedon a filament of ductile tungsten by heating the' filament in a mixtureof zirconium chloride an\d hydrogen to a temperature high enough tocause reduction of the zirconium chloride to the metal and theconsequent formation of a coating of zirconium on the tungsten filament.The resulting composite filament may be subsequently converted into ahomogeneous zirconium alloy by heatineI it to a sufficiently hightemperature to produce diffusion of the zirconium into tun sten. Myapplication Serial No. 735,075 fi ed August 30, 1924 constitutin acontinuation in part of the present app ication contains claims based onthe latter modification of my invention. Y What I claim as new anddesire to secure by Letters Patent of the United States, is 1. rlheprocess of pre aring tungsten laments containing iron w ich consists inproducing by mechanical workin filamentary bodies of ductile tungsten,eating said bodies in hydrogen to a temperature of about 1000 to 1300 C.to remove surface impurities, electroplating the cleaned tungsten `bodyWith iron, removing excess electrolyte,

and finally producing a homogeneous alloy by heating to a temperature ofat least about 1600o C.

2. The process of preparing a li hting filament consisting or tungstenan iron which is homogeneous throughout which* consists in providing uon a tungsten filament a coating of metal ic iron in measured amount andthereupon heating the coated filament to a temperature of about 1600 C.for a suliicient length of' time to produce diffusion of the ironthroughout the tungsten.

3. The process of preparing a filament constituted of a' homogeneouspredetermined alloy of tungsten and iron Which consists in removingsurface impurities from a filament of ductile tungsten, electroplatingthe cleaned filament with iron in desired proportion, removing excesselectrolyte and heating to a temperature of at least about 1600o C. fora sufficient length of time to produce uniform diffusion of the ironthroughout the tungsten.

4. The process of preparing a filamentary body consisting of ahomogeneous, predetermined mixture of tun sten'and iron which vconsistsin electroplatmg a `layer of iron upon the surface of a tungsten Wireand heating said plated Wire to a temperature sufficiently high toproduce penetration of the iron throughout said tungsten Wire.

5. The method of producing a Wire consisting of a preponderant amount ofa refractory metal and a metal alloyable therewith and capable ofdiffusing therethrough Which consists in providing a Wire consisting ofa refractory metal with a coating of the alloyable metal and then heatinthe coated Wire to a tempera-ture sufliclently high to cause alloyageand diffusion of the coating metal throughout said wire.

6. The method of producing a wire consisting of a preponderant amount ofa tungsten wire with a coating of iron and 10 tungsten and a metalalloyable therewith, heating said coated wire to a temperature whichconsists in co'atin a wire consistin suiiciently high to producepenetration and of the tungsten with t e alloyablc met alloyage of theiron throughout the tungsten and then heatin the coated wire to atemwire. perature at whic alloyagc and diffusion of In witness whereof,1 have hereunto set the coating throughout said wire occurs, my handths28th day of July, 1920.

7 The process of preparing tungsten wire n containing iron whichconsists in providing GORTON R. FONDA.

